Field of the Invention
The present invention relates to a pressure reducing valve, which includes a piston that is displaceable depending on a pressure in a decompression chamber.
Description of the Related Art
As well known in the art, pressure reducing valves function to reduce the pressure of a high-pressure fluid to a given pressure. As one detailed example thereof, a pressure reducing valve of this type is disclosed in Japanese Laid-Open Patent Publication No. 2009-157692.
The pressure reducing valve disclosed in Japanese Laid-Open Patent Publication No. 2009-157692 includes a substantially rod-shaped piston disposed at an upward end of a valve element, a first helical spring, which applies a resilient biasing force to the valve element toward a valve seat (communication passage), and a second helical spring, which applies a resilient biasing force to the piston toward the valve seat (communication passage). The first helical spring and the second helical spring are compressed beforehand, so that a resilient biasing force from the first helical spring acts on the valve element, whereas a resilient biasing force from the second helical spring acts on the piston.
In the aforementioned structure, a high pressure fluid is introduced to an outlet chamber through the communication passage. When the sum of the resilient biasing force applied to the valve element from the first helical spring and the pressing force applied to the piston from the fluid exceeds the resilient biasing force applied to the piston from the second helical spring, the piston is displaced in a direction to further compress the second helical spring. As a result, the valve element is seated on the valve seat (the communication passage is closed), whereby the pressure reducing valve is placed in a closed condition. Consequently, the overly high pressure fluid is prevented from being led out from the pressure reducing valve.
On the other hand, after closure of the valve element, when the fluid is led out from the outlet chamber and the pressure inside the outlet chamber is lowered, under an action of the resilient biasing force of the second helical spring, the piston is displaced in opposition to the pressing force applied to the piston by the fluid and the resilient biasing force applied to the valve element from the first helical spring. As a result, the valve element separates away from the valve seat (the communication passage is opened), thereby placing the pressure reducing valve in an open condition, together with the second helical spring being compressed and restored to its original condition. In this case, the fluid that was introduced to the inlet chamber is led out to the exterior of the pressure reducing valve through the outlet chamber.
By displacement of the piston as described above, the fluid is led out from the pressure reducing valve in an appropriately pressure-adjusted condition.